1. Field of the Invention
This invention generally relates to ultra-hard materials and, more specifically, to ultra-hard materials having an improved degree of thermal stability when compared to conventional ultra-hard materials such as polycrystalline diamond, and that are joined to a substrate to facilitate attachment of the overall construction for use in a desired cutting and/or drilling application.
2. Background of the Invention
Ultra-hard materials such as polycrystalline diamond (PCD) and PCD elements formed therefrom are well known in the art. Conventional PCD is formed by combining diamond grains with a suitable solvent catalyst material to form a mixture. The mixture is subjected to processing conditions of extremely high pressure/high temperature, where the solvent catalyst material promotes desired intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
Solvent catalyst materials typically used in forming conventional PCD include metals from Group VIII of the Periodic table, with cobalt (Co) being the most common. Conventional PCD can comprise from 85 to 95% by volume diamond and a remaining amount of the solvent catalyst material. The solvent catalyst material is present in the microstructure of the PCD material within interstices that exist between the bonded together diamond grains.
A problem known to exist with such conventional PCD materials is that they are vulnerable to thermal degradation during use that is caused by differential thermal expansion characteristics between the interstitial solvent catalyst material and the intercrystalline bonded diamond. Such differential thermal expansion is known to occur at temperatures of about 400° C., which can cause ruptures to occur in the diamond-to-diamond bonding that can result in the formation of cracks and chips in the PCD structure.
Another form of thermal degradation known to exist with conventional PCD materials is also related to the presence of the solvent metal catalyst in the interstitial regions and the adherence of the solvent metal catalyst to the diamond crystals. Specifically, the solvent metal catalyst is known to cause an undesired catalyzed phase transformation in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of the PCD material to about 750° C.
Attempts at addressing such unwanted forms of thermal degradation in conventional PCD are known in the art. Generally, these attempts have involved techniques aimed at treating the PCD body to provide an improved degree of thermal stability when compared to the conventional PCD materials discussed above. One known technique involves at least a two-stage process of first forming a conventional sintered PCD body, by combining diamond grains and a cobalt solvent catalyst material and subjecting the same to high pressure/high temperature process, and then subjecting the resulting PCD body to a suitable process for removing the solvent catalyst material therefrom.
This method produces a PCD body that is substantially free of the solvent catalyst material, hence is promoted as providing a PCD body having improved thermal stability. A problem, however, with this approach is that the lack of solvent metal catalyst within the PCD body precludes the subsequent attachment of a metallic substrate to the PCD body by brazing or other similar bonding operation.
The attachment of such substrates to the PCD body is highly desired to provide a PCD compact that can be readily adapted for use in many desirable applications. However, the difference in thermal expansion between the PCD bodies formed according to this technique and the substrate, and the poor wettability of the PCD body diamond surface due to the substantial absence of solvent metal catalyst, makes it very difficult to bond the thermally stable PCD body to conventionally used substrates. Accordingly, PCD bodies that are rendered thermally stable according to this technique must be attached or mounted directly to a device for use, i.e., without the presence of an adjoining substrate.
Since such conventionally formed thermally stable PCD bodies are devoid of a metallic substrate, they cannot (e.g., when configured for use as a drill bit cutter) be attached to a drill bit by conventional brazing process. Rather, the use of such a thermally stable PCD body in such an application requires that the PCD body itself be mounted to the drill bit by mechanical or interference fit during manufacturing of the drill bit, which is labor intensive, time consuming, and which does not provide a most secure method of attachment.
It is, therefore, desired that an ultra-hard material construction be developed that includes an ultra-hard material body having improved thermal stability when compared to conventional PCD materials, and that includes a substrate material attached to the ultra-hard material body to facilitate attachment of the resulting compact construction to an application device by conventional method such as welding or brazing and the like. It is further desired that such a product can be manufactured cost effectively, without the use of exotic materials or manufacturing techniques.